1. Field of the Invention
The present invention relates to a liquid injecting type oil-free screw compressor having a liquid injecting passage for injecting the liquid to the inlet port of the compressor main body while controlling the flow rate of the liquid by a flow-rate control valve.
2. Description of the Prior Art
There has been known a liquid injecting type oil-free screw compressor as shown in FIG. 2, wherein there is provided a liquid injecting passage 4 for injecting a liquid to an inlet port 3 of a compressor main body 2 while controlling the flow rate of the liquid by a flow-rate control valve 1. Furthermore, there is provided a temperature controller 6 adapted to detect the gas temperature in a discharge passage 5 of the compressor main body 2 and to control the degree of opening of the flow-rate control valve 1 for controlling the injected liquid quantity to the inlet port 3 for holding the above-mentioned temperature at the gas saturation temperature.
In some gases handled by a compressor such as an off gas or a vent gas for styrene monomer, solid matters such as polymer are generated by the change of conditions caused by compression. The generation of polymer is caused particularly often by the temperature rise by compression. Therefore, in order to control the temperature of a compressed gas to be lower than a temperature at which polymer can be produced, a liquid is injected to the inlet port 3 to keep the temperature of a compressed gas at a specified value by utilizing the latent heat of the liquid. Concretely, the gas temperature in the discharge passage is kept approximately at a gas saturation temperature.
As described in the above, in the conventional device, the injected liquid quantity is specified for holding the gas temperature in a discharge passage 5 approximately at the gas saturation temperature. Inside some parts of the compressor main body 2, however, the gas temperature is considered to be higher than the gas saturation temperature, and thereby it has been impossible to avoid the generation of polymer, a solid matter.
Consequently, the above-mentioned polymer tends to adhere to the screw rotors (not shown) inside the compressor main body, thereby leading to trouble.